What is an anterior cruciate ligament (ACL) injury?

Injuries range from mild, such as a small tear, to
severe, such as when the ligament tears completely or when the ligament and
part of the bone separate from the rest of the bone.

Without
treatment, the injured ACL is less able to control knee movement, and the bones
are more likely to rub against each other. This is called chronic ACL
deficiency. The abnormal bone movement can also damage the tissue (cartilage) that covers
the ends of the bones and can trap and tear the pads (menisci) that
cushion the knee joints. This damage can lead to
osteoarthritis.

Sometimes other knee
ligaments or parts of the knee are also injured. This includes cartilage such
as the menisci, or bones in the knee joint, which can be
broken.

What causes an ACL injury?

Your ACL can be injured
if your knee joint is bent backward, twisted, or bent side to side. The chance
of injury is higher if more than one of these movements occurs at the same
time. Contact (being hit by another person or object) also can cause an ACL
injury.

An ACL injury often occurs during sports. The injury can
happen when your foot is firmly planted on the ground and a sudden force hits
your knee while your leg is straight or slightly bent. This can happen when you
are changing direction rapidly, slowing down when running, or landing from a
jump. This type of injury is common in soccer, skiing, football, and other
sports with lots of stop-and-go movements, jumping, or weaving. Falling off a
ladder or missing a step on a staircase are other likely causes. Like any other
body part, the ACL becomes weaker with age. So a tear happens more easily in
people older than age 40.

What are the symptoms?

Symptoms of an acute ACL
injury include:

Feeling or hearing a pop in the knee at the
time of injury.

Pain on the outside and back of the
knee.

The knee swelling within the first few hours of the injury.
This may be a sign of bleeding inside the knee joint. Swelling that occurs
suddenly is usually a sign of a serious knee injury.

Limited knee
movement because of pain or swelling or both.

The knee feeling
unstable, buckling, or giving out.

After an acute injury, you will probably have to stop
whatever you are doing because of the pain, but you may be able to walk.

The main symptom of chronic ACL deficiency is the knee buckling or
giving out, sometimes with pain and swelling. This can happen when an ACL
injury is not treated.

How is an ACL injury diagnosed?

Your doctor can
tell whether you have an ACL injury by asking questions about your past health
and examining your knee. The doctor may ask: How did you injure your knee? Have
you had any other knee injuries? Your doctor will check for stability,
movement, and tenderness in both the injured and uninjured knee.

You may need
X-rays, which can show damage to the knee bones. Or
you may need other imaging tests, such as an
MRI. An MRI can show damage to ligaments,
tendons, muscles, and knee cartilage.
Arthroscopy may also be done. During arthroscopy, your
doctor inserts surgical tools through one or more small cuts (incisions) in the
knee to look at the inside of the knee.

How is it treated?

Start first aid right away.
These first-aid tips will reduce swelling and pain. Use the RICE method. The
letters stand for Rest the knee, put Ice on it, use an elastic bandage to give gentle
Compression to the knee, and Elevate the leg by propping it up above the level of your
heart. And at first it's also important to move your leg as little as possible.

Take
over-the-counter pain medicine. Be safe with medicines. Read and follow all instructions on the label.

You may need to walk with
crutches and use a knee immobilizer to keep your knee still for the first few
days after the injury.

Your knee will need to be checked by your
doctor. It's important to get treatment. If you don't, the injury may become a
long-lasting problem. There are two ways to treat the injury:

Exercises and training, also called rehab. It
takes several months of rehab for your knee to get better.

Surgery. You and your doctor can decide if rehab is enough or if surgery is
right for you.

If you have surgery, you will also have several months of
rehab afterward.

Your treatment will depend on how much of the
ACL is torn, whether other parts of the knee are injured, how active you are,
your age, your overall health, and how long ago the injury occurred.

There are three main treatment goals:

Make the knee stable if it is unsteady, or at
least make it stable enough to do your daily activities.

Make your
knee strong enough to do all the activities you used to do.

Reduce
the chance that your knee will be damaged more.

How can you prevent ACL injuries?

The best way to
prevent ACL injuries is to stretch and strengthen the leg muscles, especially
the front and back muscles of the thigh (quadriceps and hamstrings).

Cause

Anterior cruciate ligament (ACL) injuries are caused when the knee is straightened beyond
its normal limits (hyperextended), twisted, or bent side to side.

Typical situations that can lead to ACL injuries include:

Changing direction quickly or cutting around an
obstacle or another player with one foot solidly planted on the ground. (This can
happen in
sports that put high demand on the ACL, such as
basketball, football, soccer, skiing, and gymnastics.)

Landing
after a jump with a sudden slowing down, especially if the leg is straight or slightly bent
(such as in basketball).

Falling off a ladder, stepping off a curb,
jumping from a moderate or extreme height, stepping into a hole, or missing a
step when walking down a staircase. Injuries like these tend to be
caused by stopping suddenly, with the leg straight or slightly bent.

Inactive people and some older adults who have weak leg
muscles may injure their knees during normal daily activities. But they usually
injure bones, not ligaments.

When contact causes an ACL injury, it
can be from playing a sport, from a sudden and severe accident, or from less
obvious contact injuries.

Chronic ACL deficiency

The main
symptom of chronic (long-lasting and recurrent)
ACL deficiency is an unstable knee joint. The knee buckles or gives out,
sometimes with pain and swelling. This happens more often over time. But not
everyone with an ACL injury develops a chronic ACL deficiency.

What Happens

If you have a sudden (acute) anterior cruciate ligament (ACL) injury, you typically know when it happens. You may feel or hear a pop, and the knee may give out, causing you to fall. The knee swells and often is too painful or unstable for you to continue any activity.

An ACL injury can cause small or medium tears of the ligament, a complete tear of the ligament (rupture), a separation of the ligament from the upper or lower leg bone (avulsion), or a separation of the ligament and part of the bone from the rest of the bone (avulsion fracture). When any of these occur, the lower leg bone moves abnormally forward on the upper bone, with a sense of the knee giving out or buckling.

How an anterior cruciate ligament (ACL) injury
is treated and how it heals depends on:

The condition of the ACL before the injury. This includes prior injuries, partial tears, ACL deficiency, and changes due to age.

The general condition and health of the rest of your
knee before this injury.

Other injuries to the knee joint, such as to
the
cartilage or
menisci, or to bones in the knee.

Your
age, how active you are, and how committed you are to treatment and
rehabilitation (rehab).

The time of diagnosis. If the ACL diagnosis is not
made soon after the injury, the knee may be further damaged with use.

An ACL injury may develop into long-lasting and
recurrent (chronic)
ACL deficiency that leads to an unstable knee-the knee buckles or gives out,
sometimes with pain and swelling. This can occur if you had an ACL injury in the
past and didn't know it or if your ACL has not been
treated or has been treated unsuccessfully. ACL deficiency can cause damage to the joint,
including
osteoarthritis. But not everyone with an ACL injury
gets ACL deficiency.

People with minor ACL injuries usually begin treatment with
a physical rehab program. Rehab exercises build strength and
flexibility in the muscles on the front of the thigh (quadriceps) and
strengthen and tighten the muscles in the back of the thigh (hamstrings). Most people return to their normal activities after a few weeks of
rehab.

More serious ACL injuries may need several
months of rehab or surgery followed by several months of
rehab to regain your knee strength, knee stability, and range of
motion.

Not all ACL injuries require surgery. But whether you have
surgery or not, you need to start strengthening your knee and regaining motion
soon after you injure it. This prepares you for your rehab program if
you choose not to have surgery. It also helps prepare the knee for surgery if
you choose to have it.

When To Call a Doctor

Call your doctor immediately if you have an injury to your knee and:

You have severe pain in your
knee.

Your knee appears to be deformed.

You have signs
of damage to the nerves or blood vessels. Signs include numbness, tingling, a
"pins-and-needles" sensation below the injury, an inability to move your leg
below the injury, pale or bluish skin, or your leg feels cold.

You have severe swelling in your knee right after the injury.

Call your doctor today if:

Your knee begins to swell within 2 hours of the
injury.

You hear or feel a pop in your knee during an
injury.

Your knee won't bear weight.

You are unable to
straighten your leg completely.

Your knee is unstable, buckles, or
gives out.

Your knee "locks" in one position.

You have
had an
anterior cruciate ligament (ACL) injury in the past,
and you have reinjured your knee.

Before your appointment, don't put weight on the injured
knee. Use crutches if you need to.
Apply ice and wrap your knee in an elastic bandage or
neoprene (synthetic rubber) sleeve. Rest and elevate the knee. Take a
nonsteroidal anti-inflammatory drug, such as ibuprofen (Advil) or naproxen (Aleve), to reduce
swelling. For more information on first aid steps, see Home Treatment.

Watchful waiting

Watchful waiting is a period of time during
which you and your doctor observe your symptoms or condition without using
medical treatment. Watchful waiting is not appropriate if knee pain is severe;
if your knee is deformed, swells, or has limited movement immediately after an injury; or if you are unable
to bear any weight because of either pain or instability.

Serious
knee injuries need to be checked for possible broken bones as well as
ligament or
cartilage damage. Whenever immediate swelling follows
an injury, there also may be torn blood vessels or damaged nerves in the knee.
Your doctor will check your knee to make sure the blood supply to your leg is
normal and the nerves are intact.

If you have occasional pain in
your knee or your knee sometimes gives way or buckles, have your doctor check
it. If you have damaged your ACL, it is important to get treatment so that your
knee is appropriately managed. This may reduce the chance that you will get
osteoarthritis in your knee.

Exams and Tests

An
anterior cruciate ligament (ACL) injury is diagnosed
through a medical history and a physical exam. A doctor who specializes
in knee injuries (for example, an
orthopedic surgeon or
sports medicine specialist) will usually be able to
accurately diagnose an ACL injury after:

Taking your
medical history. You will be asked how you injured
your knee, about your symptoms at the time of injury, whether you have had any
other knee injuries, and general questions about your health.

Checking your knees for stability, strength, range of
movement, swelling, and tenderness. Tests for stability include a Lachman test
and a pivot shift test. The Lachman test compares the degree of looseness
(laxity) in your knees.

Looking at an
X-ray, which is usually done for any knee injury if there is pain, swelling, or you cannot put your weight on the leg.
Although an ACL injury cannot be directly diagnosed by an X-ray, an X-ray can
show whether a bone is broken, any bone fragments are in the knee, the ACL
is torn from the bone along with a little piece of the bone (avulsion fracture), or blood is present in the knee
(effusion).

If you see your doctor soon after your injury, the pain
and the degree of swelling and muscle tenseness may make it difficult for your
doctor to accurately diagnose the condition.

More imaging tests

Other tests that may
help your doctor see how badly the knee is injured include:

An MRI. It can identify an ACL tear or other problems, such as meniscus tears or other ligament
injuries.

Looking at fluid in the knee

If your knee looks red, feels warm to the touch, or is very swollen, a
knee joint aspiration (arthrocentesis) may be done. This involves removing fluid from the knee joint with a needle. It
is done to:

Help relieve pain and pressure. This may make
the physical exam easier and make you more comfortable.

Check joint
fluid for possible infection or inflammation.

Look for blood, which
may mean there is a tear.

Look for drops of fat, which may mean there is a
broken bone.

Local anesthetic may be injected to reduce
pain and make the knee easier to examine.

Other tests

Arthrometric testing: In this test, your doctor uses a tool to
measure the looseness of your knee. This test is especially useful in people
whose pain or size makes a physical exam difficult. An arthrometer has
two sensor pads and a pressure handle that allows your doctor to put force on
the knee.

Arthroscopy: This can be used
to diagnose an ACL injury and as a method of
surgery. It involves inserting tools through one or more small
incisions in the knee, which allows your doctor to examine the structures inside
the knee joint, including the ACL.

Before arthroscopy, you and
your doctor will decide what will be done if certain conditions are found. For
example, you may decide in advance that if a complete tear of the ACL is found,
it will be reconstructed during the arthroscopy. Or if a more severe condition
is found, you and your doctor may agree to discuss the condition rather than
proceeding with surgery at that time.

Treatment Overview

The goals of treatment for an anterior cruciate ligament (ACL) injury are to:

Restore normal or almost normal stability in
the knee.

Restore the level of function you had before the knee
injury.

Limit loss of function in the knee.

Prevent
injury or more damage to other knee structures.

Reduce pain.

You'll need to work with your doctor to decide whether you should have several months of
rehabilitation (rehab) or surgery with rehab. Not all ACL tears need
surgery.

Using crutches and/or splints in the
first few days. If crutches or splints are used for too long,
the muscles will become weaker from too little activity. Then movement of the
knee will become stiff and restricted.

You can help prevent ACL injuries by practicing
landing with the knees bent after jumps and crouching when pivoting and
turning.

Home Treatment

If you have an acute (sudden)
anterior cruciate ligament (ACL) injury, use the
following first aid steps to reduce pain and swelling:

Rest and reduce your activity level.
If it hurts to put weight on your knee, use crutches until you can see your
doctor. Crutches can be rented from most drugstores. Crutches should not
be used for long, because a lack of activity can cause muscle tissue to waste
away and cause restricted movement of the knee.

Ice your knee. To avoid a freeze-burn, don't put the ice directly on your skin.
Put a cloth or towel between the ice and your knee.

Elevate your
knee while applying ice or anytime you are sitting or lying
down.

Wrap your knee with an elastic bandage or neoprene sleeve
(available at a drugstore). This may help ease pain during movement and reduce
fluid inside the knee. Don't wrap your knee too tightly, as this may cause
swelling below the bandage. Loosen the bandage if it is too tight. Signs of an
overly tight bandage include numbness, tingling, increased pain, and coolness
in the foot.

After diagnosis of an ACL injury, your doctor may suggest
exercises that help strengthen your leg and increase your range of motion. They
may be the start of your nonsurgical treatment program or be used to help
prepare your knee for surgery.

Medications

Nonprescription pain
medicines such as acetaminophen (Tylenol, for example) or
nonsteroidal anti-inflammatory drugs (NSAIDs), such as
ibuprofen and naproxen, are commonly used. Be safe with medicines. Read and follow all instructions on the label.

Surgery

Most surgery for
anterior cruciate ligament (ACL) injuries involves
replacing the ACL with tissue called a
graft. Usually an autograft (tendon tissue
taken from another part of the body) is used.

Repair surgery
typically is used only in the case of an avulsion fracture (a separation of the
ligament and a piece of the bone from the rest of the bone). In this case, the
bone fragment connected to the ACL is reattached to the bone.

Most ACL surgery is done by
making small incisions in the knee and inserting surgical tools
through these incisions (arthroscopic surgery). Open surgery
(cutting a large incision in the knee) is sometimes required.

Goals of surgery

The
goals of surgical treatment for ACL injuries are
to:

Restore normal or almost normal stability in
the knee.

Restore the level of function you had before the knee
injury.

Limit loss of function in the knee.

Prevent
injury or degeneration to other knee structures.

Reduce pain.

Most people who have ACL surgery
have favorable results, with reduced pain, good knee function and stability,
and a return to normal levels of activity. But some still have knee pain
and instability. Athletes and those who take part
in sports typically can return to their sports within months. But this may depend on how
intense and sports-focused the rehab was.

Exercises before surgery

Before ACL surgery, strength and motion exercises are often
done to help get the knee ready for surgery and for rehab after surgery. Surgery is followed by a short period of home exercises,
increased activity, and the use of crutches for walking.

An intensive
rehab program to strengthen the knee then begins. The rehab
program often lasts up to a year.

Surgery in children and teens

What to think about

Depending on how bad your injury is, surgery with
rehab may offer the best chance of making your knee stable again. It also may help you return to an active lifestyle without further pain, injury, or loss of
strength and movement in your knee.

If your injured knee gives out now and then (chronic ACL deficiency) and you continue to do activities that
require a stable knee, you may injure your knee again.
That may be another reason to consider surgery.

You will need to follow a rehab program whether or not
you have surgery. If you don't complete a rehab program, even with
surgery you may not regain full stability and function in your knee.

American College of Radiology (2011). ACR Appropriateness Criteria: Acute Trauma to the Knee. Available online: http://www.acr.org/SecondaryMainMenuCategories/quality_safety/app_criteria/pdf/ExpertPanelonMusculoskeletalImaging/AcuteTraumatotheKNEEDoc2.aspx.

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